1. Field of the Invention
The present invention relates to a liquid crystal display device and a manufacturing method thereof, and more particularly to a liquid crystal display device in which a predetermined distance is held between a TFT substrate and a counter substrate by a support column system and a manufacturing method thereof.
2. Background Art
In a liquid crystal display device, liquid crystal is filled in a space defined between a TFT substrate on which pixel electrodes and thin film transistors (TFT) are formed and a counter substrate on which color filters and the like are formed, and images are formed by controlling molecules of the liquid crystal using an electric field. The distance between the TFT substrate and the counter substrate is extremely narrow, that is, several microns. Accordingly, proper setting of the distance between the TFT substrate and the counter substrate is extremely important for controlling transmissivity of light through the liquid crystal.
As an example of a method for setting a distance between a TFT substrate and a counter substrate, there has been known a method which disperses beads or the like in the space formed between the substrates. However, in dispersing the beads in the space, the beads are dispersed into regions where pixel electrodes are formed and hence, there arises a drawback that light is scattered in such portions thus lowering a contrast.
On the other hand, with respect to a conventional liquid crystal filling method, there have been proposed a method in which a space defined between a TFT substrate and a counter substrate is sealed, an opening is formed in a portion of a sealing material, and liquid crystal is filled in the space through the opening, and a method in which a necessary amount of liquid crystal is dropped on a TFT substrate and, thereafter, a counter substrate is adhered to the TFT substrate in a sealed manner thus sealing liquid crystal in the space, and the like. In any one of these methods, in dispersing beads in the space, the beads move in the space at the time of dropping the liquid crystal into the space and hence, the number of beads becomes large in some places of the space and the number of beads becomes small in other places of the space. Further, the beads are also dispersed into the inside of pixel regions where light emitted from a backlight passes thus lowering a numerical aperture of a liquid crystal display device or giving rise to a possibility of lowering a numerical aperture of the liquid crystal display device.
As a method which defines a distance between the TFT substrate and the counter substrate, besides the above-mentioned example which makes use of the beads, there has been known a method which forms support columns (spacers) formed of an organic film on the counter substrate (support column system). The support columns are, in general, mounted on portions of the counter substrate where the pixel electrodes are not present, that is, portions of the counter substrate through which light from the back light does not pass. Accordingly, there is no possibility that brightness (numerical aperture) is lowered due to the presence of the support columns. Further, the support columns are fixed to the counter substrate and hence, there is no possibility that the support columns move even when liquid crystal is dropped. Accordingly, the method which maintains the distance between the TFT substrate and the counter substrate using the support columns is also preferably applicable to a system which drops liquid crystal (liquid crystal dropping sealing system).
The support columns are formed on color filters formed on the counter substrate in general and are formed using a resin. JP-A-9-49914 (patent document 1) discloses such a case.
Further, there may also be a case where a support column is formed by stacking color filters as in the case of JP-A-2003-233064 (corresponding to US patent application US2003/0156236A1)(patent document 2).
Further, there may be a case where, on a portion of a TFT substrate side with which a spacer formed of color filters is brought into contact, a pedestal is formed. The pedestal is provided for holding a distance between a TFT substrate and a counter substrate more properly by cooperatively working with the spacer. It is often the case that the pedestal is formed by making use of a projecting portion of a gate line or a drain line such as a switching element on the gate line as described in patent document 1. Further, on a surface of an insulation film on a TFT substrate side, an alignment film which adjusts the alignment of liquid crystal is formed.